This power vs. torque debate can go on and on... because neither side is wrong.

If you could only find out one thing about an engine, the HP is definitely more important than torque. It's just physics, and HP includes torque. However, to really get to know an engine, it's the area under the torque curve that matters. (it's still some form of average power, since width of the area is rpm and height is torque)

We'll just have to wait and see what the graph for the new M3/4 looks like.

Read my post again, I am referring to axle weight distribution, in response to the post I was replying to. Not overall weight distribution.

Using the centre of gravity as the referential, polar moment and axle weight distribution are not related. Polar moment depends on how weight is distributed around the centre of gravity (how much and how far). Axle weight distribution depends on the position of the centre of gravity relative to the axles.

Now under dynamic conditions, it gets more complicated, as a car does not necessarily rotate around the centre of gravity.

I don't want to get too technical here, but for those interested, there is a very good book published by the Society of Automotive Engineers called Fundamentals of Vehicle Dynamics by T. D. Gillespie that explain these principles very well (with plenty of equations ).

Still disagree. Getting way OT but...

Consider two equal masses m, a distance d apart, say equal to a wheelbase. This is an idealized two point mass "car". This results in 50:50 weight distribution and the polar moment I(about cg) = m d^2/2. Alter the weight distribution radically so 100% is on one axle. Weight distribution = 100:0, total weight unchanged. Now here I(about cg) = 0. For the more general case you can solve for the generalized I about the cg for any value of m1 and m2.

I = (m1 m2 d^2)/(m1+m2)

Again even though m1+m2 is fixed change their ratio and you can compute exactly how I changes.

Through this simple example you should be able to see that axle weight distribution and polar moment are intricately linked. You can extrapolate to the case of a continuous variation in mass along the length rather than two point masses. In both cases though change one and you change the other. In the simple cases there will be an analytical solution, in the general case certainly not.

This power vs. torque debate can go on and on... because neither side is wrong.

If you could only find out one thing about an engine, the HP is definitely more important than torque. It's just physics, and HP includes torque. However, to really get to know an engine, it's the area under the torque curve that matters. (it's still some form of average power, since width of the area is rpm and height is torque)

Keeping in the segueing theme here...

I not so sure if the area under the torque vs rpm curve has any particular meaning. Sure more is better but that is almost the same as saying more power at all rpms is better (or more torque...).

What does have a meaning is the integral in time of torque x rpm (well in SI units torque x ω, but the same thing if you have consistent units). This gives the total work done by the engine or equivalently how much change in kinetic energy has been given to the vehicle. From that you get exactly how fast it is going. The key thing is you need to plot torque vs. time, not torque vs. rpm. There is a key shortcut here as well though because power is just torque x ω (again basically torque x rpm but in SI units). Thus you can time integrate power instead of messing with torque and rpm! Power is fundamental!

Knowing power is absolutely more fundamental as it does not matter what the gear/final drive ratios are. But of course if you know the full torque curve vs. rpm then you can get the full power curve. You just CAN NOT use crank torque alone in many equations to determine speed or acceleration where you can use power alone! That's the power of power.

As a e92 m3 owner I understand that it's early so I'll wait and see what the final numbers are but what they are coming up with now in my opinion is not enough coming from a e92 m3 I'm not the tuning type and if the new m3 is around 80k and has the same hp I won't be trading in my e92 for it I
Feel like its not enough to make me trade or upgrade to it. I understand that the m3 is about more than straight line performance I love my m3 but if the figures stay true to this thread then I don't need the new m3......

Consider two equal masses m, a distance d apart, say equal to a wheelbase. This is an idealized two point mass "car". This results in 50:50 weight distribution and the polar moment I(about cg) = m d^2/2. Alter the weight distribution radically so 100% is on one axle. Weight distribution = 100:0, total weight unchanged. Now here I(about cg) = 0. For the more general case you can solve for the generalized I about the cg for any value of m1 and m2.

I = (m1 m2 d^2)/(m1+m2)

Again even though m1+m2 is fixed change their ratio and you can compute exactly how I changes.

Through this simple example you should be able to see that axle weight distribution and polar moment are intricately linked. You can extrapolate to the case of a continuous variation in mass along the length rather than two point masses. In both cases though change one and you change the other. In the simple cases there will be an analytical solution, in the general case certainly not.

Good book by the way!

The flaw in your example resides in the fact that you consider the masses limited to be directly over the axles.

Take your example of the two mass car but instead of combining both masses over one axle, combine them right in the middle of the two axles. You would also reduce I to zero but would maintain the 50-50 weight distribution.

As another example, let's assume a car of a given weight and polar moment. If the axles are positioned at equal distance from the centre of gravity, the car has a 50-50 weight distribution. Moving the front axle forward (assuming negligeable mass for the axles themselves) will shift the weight distribution towards the rear axle, but the polar moment around the CG remains unaltered.

In both examples one parameter could be changed without impacting the other.

I not so sure if the area under the torque vs rpm curve has any particular meaning. Sure more is better but that is almost the same as saying more power at all rpms is better (or more torque...).

What does have a meaning is the integral in time of torque x rpm (well in SI units torque x ω, but the same thing if you have consistent units). This gives the total work done by the engine or equivalently how much change in kinetic energy has been given to the vehicle. From that you get exactly how fast it is going. The key thing is you need to plot torque vs. time, not torque vs. rpm. There is a key shortcut here as well though because power is just torque x ω (again basically torque x rpm but in SI units). Thus you can time integrate power instead of messing with torque and rpm! Power is fundamental!

Knowing power is absolutely more fundamental as it does not matter what the gear/final drive ratios are. But of course if you know the full torque curve vs. rpm then you can get the full power curve. You just CAN NOT use crank torque alone in many equations to determine speed or acceleration where you can use power alone! That's the power of power.

Exactly!

That is why torque by itself is useless........ Torque is a static measure of the amount of weight the crankshaft could lift if it had a lever 1 foot long on the end of it (I know you know this but many people don't) hence the unit Lb/Ft. Torque can't do work or accelerate an object unless it it delivered over time.

In my main area of knowledge, diesel engines, horsepower is the way all engines are rated, the torque numbers are mentioned of course, but in reality, the amount of horsepower the engine produces determines the amount of work it can do, not the amount of torque it produces. Everyone knows that diesels make huge torque numbers. For example, a Detroit Diesel Series 60 14L engine makes 1650 Lb/Ft @ 1100 RPM yet only makes 515 HP @ 1800RPM in it's most aggressive factory rating. http://www.demanddetroit.com/pdf/Eng..._S60_specs.pdf

So the moral of what I am saying is that torque is good but unless it can be maintained across a broad RPM range you can't make much horsepower with it. You can't make horsepower without torque, but torque itself can't perform work. A torquey engine is nice, but unless that torque curve is broad, the average horsepower output of the engine is many times not as good as an engine with a lower peak torque number and a broader/flatter torque curve.

trust me, it's damn hard to overcome the S65 NA V8...
Not only it being advertised "the last NA BMW M made", this is probably the best engine BMW has ever produced...both in production stand point and racing field/world

Not only that it appears to be the last NA BMW engine period - at least for now

Torque is physical characteristic of the engine (at the output axle). as is rpm, but as a 'number' it is only relevant WITH rpm, because 'torque' is simply the physical force of the engine at its output, which can be manipulated any way you want, with gear/levers.. hence it MUST be stated WITH rpm (as HP, or power) otherwise it it truly meaning less.
Why it SEEMS relevant, is because turbo engines give high torque at low rpm, which is the equivalent of high HP at low rpm (the two are identical). The same with diesel engines. So it is a characteristic of the physical setup (NA vs turbo, diesels) which give higher power at low rpm (=high 'torque' at low rpm).
That said, it is a misleading number, as it leads people to draw wrong conclusions - but it is given simply as a statistic of the engine, for engineers to use.
So if you want to talk about something that is accurate, you should talk about HP@rpm (=torque*rpm@rpm), or if you want to see how fast a car is, you also consider how fast it revs.

Torque is physical characteristic of the engine (at the output axle). as is rpm, but as a 'number' it is only relevant WITH rpm, because 'torque' is simply the physical force of the engine at its output, which can be manipulated any way you want, with gear/levers.. hence it MUST be stated WITH rpm (as HP, or power) otherwise it it truly meaning less.
Why it SEEMS relevant, is because turbo engines give high torque at low rpm, which is the equivalent of high HP at low rpm (the two are identical). The same with diesel engines. So it is a characteristic of the physical setup (NA vs turbo, diesels) which give higher power at low rpm (=high 'torque' at low rpm).
That said, it is a misleading number, as it leads people to draw wrong conclusions - but it is given simply as a statistic of the engine, for engineers to use.
So if you want to talk about something that is accurate, you should talk about HP@rpm (=torque*rpm@rpm), or if you want to see how fast a car is, you also consider how fast it revs.

Excellent post. 100% agree. I was actually thinking of adding the exact same comment during one of these all too often hp vs. torque debate. It is absolutely amazing how many car guys completely misunderstand the differences.

Excellent post. 100% agree. I was actually thinking of adding the exact same comment during one of these all too often hp vs. torque debate. It is absolutely amazing how many car guys completely misunderstand the differences.

Did you see my post above?

Check out the dynographs in the link and you can see how lots of torque can deliver small horsepower numbers, or rather, do little amounts of work. There are software/fuel injector/pump/turbo upgrades (aftermarket and OEM) available for small, and medium sized diesel engines. Many of these upgrades aren't aimed at increasing the peak torque numbers too much (they sometimes do increase a little bit but are controlled by the computer to a max number), but are aimed at making more torque higher in the RPM range. By not increasing peak torque numbers greatly, you are not increasing the BMEP's or IMEP's that the engine components are subjected to beyond design specs. Because of the multiplication effect that RPM's have on torque's ability to produce horsepower, holding that same peak torque higher into the RPM range allows lots more horsepower to be delivered without stressing the engine too greatly.

Torque is force, and force can't achieve any work unless there is movement measured over a time. This is what everyone needs to understand. Even when an engine is "torquey" the acceleration it achieves totally dependant upon the amount of horsepower that the torque develops at a specific RPM.

+1 not impressed at all. looks like I'm going GTR after this lease is up.

Sorry for the slightly OT post.

My M3 lease is up in August 2013, so I'm also trying to figure out my next step. Aside from performance, could you live with a GT-R? I've asked myself the same thing and I'm not sure I could. The GT-R is great, don't get me wrong. But, the interior is pitifully subpar and tiny. My previous car was a 335ix and I seriously considered the GT-R, but ended up with the M3. Keep in mind, my M3 is my DD; I don't have another car.

Too little.
With n54 engines able to produce numbers in that range without a lot of work, this does not seem compelling. We are talking somewhere in the neighborhood of 65-70 large for one that isn't even maxed out with options.

Sorry, but the M5 got a real HP and torque bump.
This isn't anything to write home about. Not impressed......

Thats exactly my thoughts. I already have more than that under the hood of my N54 E92. I also have an LSD, so really not compelling in my case. Delivery is very factory-like too. BMW already knows whats been done out there with these engines so it begs the question.

Consider two equal masses m, a distance d apart, say equal to a wheelbase. This is an idealized two point mass "car". This results in 50:50 weight distribution and the polar moment I(about cg) = m d^2/2. Alter the weight distribution radically so 100% is on one axle. Weight distribution = 100:0, total weight unchanged. Now here I(about cg) = 0. For the more general case you can solve for the generalized I about the cg for any value of m1 and m2.

I = (m1 m2 d^2)/(m1+m2)

Again even though m1+m2 is fixed change their ratio and you can compute exactly how I changes.

Through this simple example you should be able to see that axle weight distribution and polar moment are intricately linked. You can extrapolate to the case of a continuous variation in mass along the length rather than two point masses. In both cases though change one and you change the other. In the simple cases there will be an analytical solution, in the general case certainly not.

The flaw in your example resides in the fact that you consider the masses limited to be directly over the axles.

Take your example of the two mass car but instead of combining both masses over one axle, combine them right in the middle of the two axles. You would also reduce I to zero but would maintain the 50-50 weight distribution.

As another example, let's assume a car of a given weight and polar moment. If the axles are positioned at equal distance from the centre of gravity, the car has a 50-50 weight distribution. Moving the front axle forward (assuming negligeable mass for the axles themselves) will shift the weight distribution towards the rear axle, but the polar moment around the CG remains unaltered.

In both examples one parameter could be changed without impacting the other.

Good counterpoints. Although I would say these are somewhat special cases. Let me restate. You stated polar moment and axle weight distribution are not related. My counterpoint showed that in some cases they certainly are related, although I over generalized to which you provided counterpoint.

Arbitrary changes in the density (or mass) distribution in a vehicle will change its axle weight and will change it polar moment as both are sums (integrals) of the density distribution. Also, a more even axle balance (at a given fixed weight) produces a lower I whereas a more unbalanced axle ratio will produce a lower I (that comes from the simple formula I provided prior).

N54 owners who bolt on a single 62mm hairdryer are going to slapping the new M3 silly. Where are all the fanboys now who said the E9x had plenty of torque?

You must recognize how silly this comparison is...

1. Stock to modded, always a lame comparison.
2. More apples to apples might be a software only modded F82 M4 vs. software only modded N54 3er. The M will destroy it.
3. Another comparison might be on the track vs. a drag race. The cars are more designed for the former.
4. Crank torque is meaningless. Power is what dictates acceleration at any speed in any gear.
5. The E9X M3 puts more torque to the wheels than many modified N54 3ers and this beats them in races. That is because it makes more power. Sure extensively modded N54s can out drag an E9X M3, no big surprise there.

N54 owners who bolt on a single 62mm hairdryer are going to slapping the new M3 silly. Where are all the fanboys now who said the E9x had plenty of torque?

LOL! It amazes me that people still try to compare a modded car to a stock one.
I can slap a Hayabusa 1300cc motor into a smart car and it will spank your precious little 335 all day long -> 0-60, 1/4 mile etc.. How about an STI with a chip and down pipe compared to your stock 335?
We can make other comparisons? Does any of that make sense yet?